This invention relates to electric hot water heaters of the dual element type, and more particularly to an electrical control circuit by which to minimize the cost of operation of such heaters.
Hot water heaters of various types heretofore have provided means by which to minimize energy costs. For example, U.S. Pat. No. 4,371,779 provides means for sensing the flow of water to or from the hot water tank to activate the heater mechanism which may be a single electric heater or an electrically controlled combustion burner. U.S. Pat. Nos. 4,413,775; 4,166,944; and 4,016,402 disclose the control of hot water heaters by sensing the temperature of incoming cold water and/or outgoing hot water.
U.S. Pat. No. 3,329,800 discloses a type of electric hot water heater provided with dual electric heaters wherein the top and bottom heaters are controlled independently and automatically by separate thermostats, the bottom heater being used to maintain water in the lower part of the tank at a temperature somewhat lower than the water in the upper part of the tank. U.S. Pat. No. 1,712,931 discloses a type of electric hot water heater of the dual heater type wherein the smaller upper heater element is used as the primary source of heat for a small upper quantity of water, and a manual switch is provided to energize a larger lower heater element for large capacity demand, it being required that the manual switch be opened to de-energize the lower heater when the large hot water capacity is no longer needed.
Other hot water heaters provided with similar manual and automatic controls are disclosed in U.S. Pat. Nos. 1,892,557; 2,480,302; 2,834,865; 3,162,752; 3,353,001; 3,484,580; 4,058,702; 4,267,432; and 4,324,207.